This case study was written at the time when OneSteel was part of BHP. In that
context, in some instances within this case study, reference may be made to BHP.
Steel provides pleasant
promenades in
Karrinyup
Karryinyup, 8 kilometres North West of
Perth, is generally considered to be one of the
city’s most desirable suburbs. Karrinyup’s
shopping centre represented a contradiction
to the premium locality. It was old and did not
capitalise on its location. Its potential however
was recognised by developer Schroders.
Costing $68 million, and estimated to take
two-and-a-half years to fully redevelop, the
centre is shaping up to be a ‘must’ for the
discerning shopper.
As with most shopping centre redevelopments, it was essential that reconstruction work
was carried out while the centre remained
functional in order to minimise loss of trade to
remaining tenants and minimise inconvenience
to shoppers. This requirement called for careful
planning by the contractor and the consulting
team and was facilitated by dividing the project
into three stages:
• Stage One involved demolition of the existing
shopping mall between Myer and Aherns
department stores and the reconstruction of
a two level shopping mall. The number of
speciality shops in the mall was expanded
from 70 to 150 shops.
• The second stage added a new restaurant
court to the North East area of the site and an
elevated car park.
• The final stage is currently under construction and includes refurbishment of the old food
court as a fresh food centre and an extension
of Woolworths.
Superior open space environment
The two level shopping centre is constructed
of structural steel columns supporting an in-situ
slab. Column grids were constructed on the old
6 x 6 metre grid (approximately), throughout
the lower level. However, on the upper level,
only one column every second grid was
required. Most columns were incorporated in
the tenancy walls, a key benefit of utilising
North elevation
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structural steel. This feature
maximised both available space and
clear space, which in turn contributed to heightened aesthetic appeal
of the centre.
To maximise construction speed
on site, the lower and upper level
columns, 150SHS and 100SHS
respectively, were splice welded
together with a cap plate and lifted into place
as a two storey column. In-situ slabs were
supported off the columns at the first level via
cast in lugs which were welded under the
column splice cap plates.
In keeping with the architect’s vision of an
open, light and attractive shopping environment, the centre has ‘promenades’, unlike a
traditional mall. The promenades have been
created by eliminating the first floor walkway
soffit and having a parapet to the shopfronts.
The ceiling springs from well behind the
parapet, supported by 3-dimensional trusses
which taper in both planes towards the centre
of the arch. These structural trusses are light
and open in nature, a system made possible
by external supports.
The architect’s vision in using a triangulated
truss system to support the roof in the promenade was one of the challenges faced by the
engineers. After investigating various steel
sections for the chord members, Peter Reynolds
of Connell Wagner noticed a Hexagonal bar on
the front cover of an old BHP Steel catalogue,
which suited the inclined struts coming into a
perpendicular face. The 63mm Hexagonal bars
separated by struts, (25mm square rods), were
used for all the 24 metre long arches. In between
these struts were a series of corner and centre
rings joined by diagonal rods. Whilst at the
ends where the distance between chord
members is shallow and where the mall
glazing was supported, 4mm steel plates were
used. The hoop pine plywood ceiling was
supported on metal framing channels above
the trusses.
Part of the COLORBOND® roof profiles were
to be sprung curved to a 120 metre radius,
however this presented a challenge, as the
manufacturer’s product information nominated
a maximum 60 metre radius. BHP Building
Products overcame this restriction by using
a lower tensile G300 profile Klip-Lok 406,
Colorbond XRW, and demonstrated the
required radius on a test rig.
Speedier construction with steel
In the first stage, protection was provided
by a 7 metre wide access walkway, comprising
steel portals and precast planks. This secured
a safe pedestrian walkway from Myer to the
central promotional area. This meant that
demolition above the walkways could proceed
whilst people continued to shop. Mobile cranes,
on either side of the walkway, were used to
erect the trusses which were then temporarily
propped in the middle with scaffold towers
which were supported on top of the temporary
structure. The trusses were then butt welded
together with a 25mm thick plate to form the
arch. The ends of the arches were connected
to the lower roof and the load was transferred
down to the firewall at the corridor. Whilst
commencing the next stage, the two level retail
centre was in operation.
A similar construction method was used for
the second part of phase one, from Aherns to
the central promotional area. To save time on
site, the trusses were welded together on the
ground and lifted with a spreader beam to final
position. A Leibherr hammer head electric
tower crane on 50m long rails was used for this
operation due to a lack of access for mobile
cranes on one side of the walkway. This enabled
work to proceed on both sides of the enclosed
pedestrian walkway at the same time enabling
practical completion to be one week early.
John Flecker of Multiplex Constructions
commented that he was pleased with the speed
of steel fabrication in the project. With the
majority of structural steel already fabricated
during the first phase of stage one, it was
immediately available for erection during the
second phase; a time-saving bonus.
The upper mall features 8.6m wide voids
with 4.5m suspended walkways on either side.
The bridges between the voids connecting the
suspended paths are supported by a 3-dimensional truss similar to those of the ceiling.
The central promotional area is essentially
a dome structure, supported on similar triangulated trusses emanating from the four corners.
A feature above this area is the flagpole support
structure made of 323.9 x 6.4CHS Grade 350
and braced with 24mm round bars connected
to the lower roof structure.
North-East Carpark:
Engineers Connell Wagner investigated
several options for the carpark design, and
realised a 10% deck saving by incorporating
a 17 metre clear span structure, avoiding any
loss of space due to internal column widths.
Overall dimensions of the elevated carpark are
104 metres long and 51 metres wide.
The carpark structure is made up of steel
columns and beams supporting Double-T
precast concrete beams. East-West frame action
is provided with two internal rows of 610UB125
Upper level view of mall, towards central promotions area
beams and 530UB82 edge beams in
300PLUS®, supported over 355.6x12.7CHS
Grade 350 single level columns spaced every
three car bays, 7.5 metres apart. The 15 metre
long steel beams were erected continuously
over two columns and connected to adjoining
members with simple pin web splices near the
point of contraflecture.
Full height stiffeners were used in steel
beams over columns to transfer floor load and
provide beam stability during erection. Steel
beams were then fixed with four M24 bolts
on capped columns.
In the North-South direction, lateral
resistance was provided with shear walls and
the ramp structure. The Double-T beams span
17m between steel beams and are 2.6m wide
and 500mm deep with 80mm thick slab. The
precast beams were notched to 180mm thick
and placed on 75mm x 10mm thick Granor
Bearing Strips which were glued on top of the
steel flanges.
Camber tolerances varied with the precast
units and they were clamped back together at
the top to even out the floor level. Drainage
required a 1 in 100 fall to the north and south
of the centre of the deck and this was achieved
by setting down the end steel beams by 100mm.
The precast units were then sealed and the
electrical services and F81 fabric were placed
on deck and covered with the required topping.
Precast planters were used at deck perimeter.
The ramp however comprised of 460UB67.1
end beams supporting 200mm thick precast
panels and 50mm thick topping.
The steel frame was erected very quickly
with a 20 tonne capacity mobile crane, whilst
the precast units were erected over a two month
period as production allowed. Each plank was
bolted in place on 125 x 125 x 8mm EA erection
angles welded to edge of beam flanges.
Peter Reynolds of Connell Wagner said that,
“Overall efficiency of structure was achieved,
minimum mass solution was not necessary
and the beam arrangement had simple
connections”.
Design Software
All steelwork was designed to AS4100.
SpaceGass was used to do analysis and
Limsteel for design. Drafting was done on
Autocad. This enabled the information to flow
from architect to engineer to fabricator shop
detailer. Project architect Duncan Jordan of
Cameron Chisholm & Nicol said that the ability
to fine tune drawing details via computer and
then to look at buildability and adjust aspects
of the design, for example the rings in the
trusses, made the project considerably easier.
Fabrication
Terry Condipodero of Allcon Steel Construction said that the fabrication of the trusses
required a suitable jig to cater for the varied
radii along the truss. One truck could accommodate three trusses on jigs, firstly to the paint
shop and then to site.
A total of 650 tonnes of steel was fabricated
for the project by Allcon with 107 tonnes
required for hexagonal bar chords of the trusses.
Surface treatment
The carpark steelwork was abrasive blast
cleaned to Class 2 finish and painted with 75mµ
of Inorganic Zinc Silicate. The exposed steel
trusses inside the shopping centre had the same
base treatment but were finished with
Taubman’s Interprime and sun proof acrylic
low sheen in pendulum dark green.
Conclusion
Project Manager Doug Hellens of PenLas
said the lightweight steel roof trusses were
innovative and aesthetically pleasing, offering
the solution to the open promenades. The small
steel columns provided added flexibility,
meeting the leasing agent’s need of some
column-free shops.
Developer:
Project Manager:
Architect:
Engineer:
Contractor:
Fabricator &
shop detailing:
Erector:
Distributors:
Schroders, on behalf of
Perpetual Trustees Co. Ltd.
as trustee for KSC Trust
PenLas
Cameron Chisholm & Nicol
Connell Wagner
Multiplex Constructions
Allcon Steel Construction
Perth Rigging
Steelmark Eagle & Globe
Tubemakers Steel
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